Powdery mold-releasing lubricant for use in casting with a mold and a mold casting method

ABSTRACT

A powdery mold-releasing lubricant according to the present invention uses a powdery mixture of a powdery organic material, which is evaporated or decomposed by heating to generate a gas, and a powdery inorganic material. A gas-solid mixed layer formed with the gas generated from the powdery mixture and the powdery inorganic material is used as a heat-insulating boundary layer. The powdery mold-releasing lubricant is inexpensive and has a superior mold lubricity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a powdery mold-releasing lubricant and a moldcasting method, and particularly intends to advantageously improve moldlubricity by effectively combining a powdery organic material which isdecomposed or evaporated by heating with a powdery inorganic material.

2. Description of the Related Art

A powdery inorganic material having superior heat insulation and heatretention, such as talc, is used as a powdery mold-releasing lubricantin mold casting processes to reduce a flow rate of heat from a moltenmetal to a mold. However, in recent years, it is desired to develop sucha mold-releasing lubricant that uses an inexpensive powdery inorganicmaterial which does not necessarily have high heat retention to reduce amanufacturing cost of the mold-releasing lubricant.

That is, conventional powdery mold-releasing lubricants have utilizedinsulating properties of inorganic materials for heat retention of themolten metal, but selection latitude of the inorganic materialsavailable for mold casting have been limited because of a limitation ofpowdery inorganic materials with good heat-insulation properties. Forexample, graphite is an inexpensive material and has good solidlubricity. However, since graphite is an electric conductor, its heatconduction caused by motions of free electrons is extremely high ascompared to inorganic materials such as oxides, which posses a problemupon heat-insulating property, therefore, graphite cannot be used forsuch applications that require of heat insulation or heat retention.

As a solution for the above problem, it is considered to use a gasgenerated by decomposition or evaporation of a material consisting apowder as a heat-insulating boundary layer between the mold and themolten metal instead of utilizing the heat-insulation property of theinorganic material itself. However, it is practically impossible to forma thin heat-insulating boundary layer without any discontinuity betweenthe molten metal flowing in the casting process and the mold from thegas generated by decomposition or evaporation of the organic materialsalone.

SUMMARY OF THE INVENTION

The present invention has been developed in due consideration of theabove situations. An object of the present invention is to provide apowdery mold-releasing lubricant which is inexpensive and has a goodmold-releasing lubricity as well as a mold casting method using such apowdery mold-releasing lubricant.

The present inventors have strenuously repeated the study to achieve theabove object. As a result, it is found that the desired object can beadvantageously achieved by combining a powdery organic material which isdecomposed or evaporated by heating with a powdery inorganic material.

That is, it is found that by mixing a powdery inorganic material and apowdery organic material, a movement of a generated gas is restrained(pinned) with the powder of an inorganic compound, and, as a result, auniformly thin heat-insulating boundary layer is stably formed withoutany discontinuity between a mold or a sleeve and a molten metal. Herein,the powdery inorganic material is intended to pin the gas generated byevaporation or decomposition of the powdery organic material to formuniformly thin heat-insulating layer, not to secure the heat-insulatingproperty as in the conventional lubricant.

Although a variety of methods for improving lubricity by mixing powdershaving different properties have been proposed, among such solidlubricants, there is no example that actively use the generated gas toimprove the lubricity.

The gist and the constitution of the invention are as followed. 1) Apowdery mold-releasing lubricant for use in casting with a mold,comprising a powdery mixture of a powdery organic material which isevaporated or decomposed by heating to generate a gas and a powderyinorganic material.

2) In the above 1), the powdery inorganic material is a powder of aninorganic material having a solid lubricity, said inorganic materialbeing selected from the group consisting of graphite, kaolinite, SHIRASU(pumice stone) balloons, mica, zirconium silicate, carbon nanotube,carbon isotopes, talc, pyrophylite, crystalline SiO₂, magnesium oxide,zirconium silicate, perlite and vermiculite.

3) In the above 1), the powdery inorganic material is a powder of aninorganic material having a solid lubricity, said inorganic materialbeing selected from the group consisting of graphite, kaolinite,SHIRASU(pumice stone) balloons, mica, and zirconium silicate.

4) In the above 1) to 3), a mixed rate of the powdery organic materialin the mixture is such an amount that can generate 10-50 ml of a gas per1 g of the mixture.

5) In the above 1) to 4), an average particle size of the powderyinorganic material in the mixture is 1-30 μm.

6) In the above 1) to 5), the powdery organic material is selected fromthe group consisting of polyethylene wax, metal soap, paraffin carbonhydride, sulfonic acid and sulfonic acid salt.

7) A mold casting method, comprising the steps of applying a powderymold-releasing lubricant in the above 1) to 6) onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.

8) In the above 7), an amount of the powdery mold-releasing lubricantapplied on the internal surfaces of the molding cavity and/or theinjection sleeve is 0.01-10 g per 1 m² unit area of.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

In order to explain the invention, reference is made to the accompanyingdrawings, in which:

FIG. 1 is a schematic sectional view comparing (a) a case when themixture of the powdery organic material and the powdery inorganicmaterial according to the invention is used as a lubricant, and (b) acase when only the powdery organic material is used as a lubricant;

FIG. 2 is a graphical representation showing the relationship between arate of the powdery organic material in the mixture and a flow length ofa molten aluminum alloy;

FIG. 3 is a schematic diagram showing a mold casting device used in theexample of the invention for confirming a presence of a heat-insulatingboundary layer between a casting mold and a molten metal;

FIG. 4(a) to FIG. 4(c) are microscopic photographs in the case that amixture of a powdery organic material and a powdery inorganic materialaccording to the invention are used as a lubricant, which illustrate aforming state of a heat-insulating boundary layer comprising a mixedlayer of a generated gas and the powdery inorganic material, and acontacting state between the molten metal and the internal surface ofthe mold; and

FIG. 5(a) to FIG. 5(c) are microscopic photographs in the case that onlya powdery organic material is used as a lubricant, which illustrate aforming state of the heat-insulating boundary layer of a generated gas,and a contacting state between the molten metal and the internal surfaceof the mold.

DETAILED DISCRIPTION OF THE INVENTION

According to the present invention, a particularly superior heatinsulation is not necessary for the inorganic material itself, because agas generated by evaporation or decomposition of the organic material isused as a mean of reducing a flow rate of heat from the molten metal tothe mold. Therefore, selection latitude of powders is widely expanded,and a powder of a low cost inorganic material may be used.

Since the powdery inorganic material does not act as an insulator butprimarily as a material for pinning the generated gas, the powderyinorganic material itself may have a low insulation property, andpreferably has a superior solid lubricity to prevent an adhesion withthe mold. For example, graphite, kaolinite, SHIRASU balloon, mica, boronnitride and the like are particularly advantageously suited. Moreover,the powdery inorganic material is not limited to the above materials,but carbon nanotube, carbon isotopes such as C₆₀, talc, pyrophylite,crystalline SiO₂, magnesium oxide, zirconium silicate, perlite,vermiculite may preferably be used.

On the other hand, as the powdery organic material, any kind ofmaterials that is in a solid state at the room temperature and generatea gas by evaporation or decomposition by heating can be used. Inaddition, the material itself is not necessary to have a lubricity atthe solid state. Polyethylene wax, metal soap (Ca, Zn and Li soap) andthe like are advantageously suitable for such a powdery organicmaterial. Other than the above materials, paraffin carbon hydride,sulfonic acid, sulfonic acid salt or the like may preferably be used.

A method for producing the powdery mold-releasing lubricant is notparticularly limited, but the lubricant may be produced by mixing thepowdery organic material and the powdery inorganic material havinggrinded or sorted into the preferred particle size. The lubricant mayalso be produced by grinding or sorting a powdery mixture of the powderyorganic material and the powdery inorganic material.

As mentioned above, when only the powdery organic material is used asthe lubricant, i.e. only the generated gas is used, it is practicallyimpossible to form a thin heat-insulating boundary layer without anydiscontinuity between the molten metal and the mold. On the contrary,according to the invention, when the mixture of the powdery organicmaterial and the powdery inorganic material is used as the lubricant,the gas generated by evaporation or decomposition of the powdery organicmaterial is pinned by the powdery inorganic material to form a uniformlythin insulation layer, and thus good mold-releasing lubricity isexerted.

The above mechanisms are shown in FIGS. 1(a) and (b) as schematic viewsand will be compared and described. FIG. 1(a) illustrates a case whenthe mixture of the powdery organic material and the powdery inorganicmaterial according to the invention is used as the lubricant, and FIG.1(b) illustrates a case when only the powdery organic material is usedas the lubricant. As shown in FIG. 1 (b), when only the powdery organicmaterial is used as the lubricant, since the generated gas is dividedand a thin heat-insulating boundary layer without any discontinuity isnot formed between the molten metal and the mold, the molten metalcontacts partially with the mold, from which the heat is radiated to themold. On the contrary, as shown in FIG. 1 (a), when the mixtureaccording to the invention is used as the lubricant, since the generatedgas is pinned by the powdery inorganic material to form thinheat-insulating boundary layer without any discontinuity between themolten metal and the mold, the heat is hardly radiated to the mold.

According to the invention, when a mixed rate of the powdery organicmaterial in the mixture is too low, a sufficient heat-insulating effectcannot be acquired. On the contrary, when the rate is too high, problemssuch as involving the gas into the molten metal are concerned.Therefore, the mixed rate of the powdery organic material is preferablysuch an amount that can generate about 10-50 ml of gas per 1 g of themixture.

FIG. 2 shows results which were obtained by investigating theheat-insulating effect, when graphite was used as the powdery inorganicmaterial and polyethylene wax was used as the powdery organic material.The results are given in relation to an amount of the generated gas per1 g of the mixture. Herein, the insulation effect was evaluated on aflow length of a molten aluminum alloy, when 2 g of the mixture per 1 m²was applied on the surface of the mold and then the molten aluminumalloy was flown on it. As shown in FIG. 2, the particularly superiorheat-insulating effect is obtained where the amount of the generated gasper 1 g of mixture is 10-50 ml. More preferably, the amount is 17-38 ml.

A relationship between the flow length of the molten aluminum alloy andthe mixed rate of polyethylene wax in the mixture is also shown in FIG.2. Polyethylene wax may be included in the range from 10 to 50 mass % toobtain 10-50 ml of the generated gas per 1 g of the mixture, which isrequired to achieve a superior insulation effect, and in the range from17 to 38 mass % to obtain 17-38 ml of the generated gas which is morepreferable.

When an applicability of the mixed powder and a pinning effect of thepowdery inorganic material on the generated gas are taken intoconsideration, the particle size of the powdery inorganic material inthe mixture is also important. The inventors investigated this point andfound that a good result is obtained when the average particle size ofthe powdery inorganic material is 1-30 μm. The particle size of thepowdery organic material is not particularly limited, but 1-30 μm, sameas the powdery inorganic material, is preferable since the powderabsorbs many water molecules and as a result aggregation of the powdertends to occur to lower the applicability to the mold when the particlesize is too much small, and especially for an aluminum alloy, smoothnessof the surface of the casting is lowered to result in a nonconformingproduct when the particle size is too much large.

Moreover, although an applying method is not particularly limited whensuch mixture is to be applied on the internal surface of the moldingcavity for mold casting or that of the injection sleeve, such a methodthat the mixture is introduced into the mold with air by a vacuumsuction method to be adhered on the surface of the mold isadvantageously suited in the case of the mold being closed. On the otherhand, such a method that the mixture is blown or is adhered on thesurface of the mold by an electrostatic power is advantageously suitedin the case of the mold being opened.

In addition, the amount of the applied powder is not particularlylimited, but about 0.01-10 g per 1 m² is preferable. Because asufficient insulation effect cannot be achieved when the amount of theapplied powder is less than 0.01 g/m², and an involvement of the gasinto the molten metal is concerned when the amount of the applied powderis more than 10 g/m². More preferably, the amount is in the range from0.5 to 2.0 g. The mold casting according to the present invention refersto all the castings that cast with molds such as a die casting, agravity casting and high-pressure casting.

In this way, according to the present invention, a uniformly thinheat-insulating boundary layer comprising the mixed layer of the powderyinorganic material and the generated gas is formed between the castingmold or the sleeve and the molten metal, when the mixture is contactedwith the molten metal during the casting process. Therefore, while themolten metal floats and flows on the solid-gas mixed layer without adirect contact with the mold or the sleeve, the molten metal is filledin the cavity, therefore, the flow rate of heat from the molten metal tothe mold or the sleeve is remarkably reduced.

EXAMPLE

Polyethylene wax having the average particle size of 5 μm and graphitehaving an average particle size of 11 μm were used as the powderyorganic material and the powdery inorganic material, respectively, andwere mixed to give a rate of the powdery organic material in the mixtureto be 25 mass %. The rate of the powdery organic material wascorresponding to 30 ml of an amount of the generated gas per 1 g of themixture. The mixture was introduced into the mold shown in FIG. 3 withair by a vacuum suction method to be adhered on the surface of the moldat a rate of 2 g/m². Then a molten aluminum alloy of 650° C. wasinjected into the mold.

A formation of the heat-insulating boundary layer comprising the mixedlayer of the generated gas and the powdery inorganic material wasdirectly observed by using a zoom microscope and super-high-speed videophotography with a mold having a quartz glass window. The boundarylayer-forming state with the lapse of the time are shown in FIGS. 4(a),(b) and (c). As shown in the figures, when the mixture according to theinvention was used, a uniformly thin heat-insulating boundary layercomprising the mixed layer of the powdery inorganic material and thegenerated gas was formed on the surface of the mold. For comparison, theformation of the heat-insulating boundary layer was investigated whenonly the powdery organic material was used, and results are shown inFIGS. 5(a), (b) and (c). As shown in the figures, in this case, althoughsome regions where the molten metal was floated by the generation of thegas could be seen, the molten metal was contacted with the mold over awide region.

Then, in the same manner as aforementioned, it was examined how thin thecasting products could be produced. As a result, it was confirmed that athin, large product of an aluminum alloy having a thickness of 0.5 mmand an area of 1 m² could be cast by forming the heat-insulatingboundary layer according to the present invention.

As having been described above, according to the present invention, byusing the mixture of the powdery organic material which generate the gasby evaporation or decomposition by heating and the powdery inorganicmaterial as the mold-releasing lubricant, a thin heat-insulatingboundary layer can be formed without any discontinuity between themolten metal and the mold. Further, because of an improvement of theheat retention in the sleeve or the casting mold, a thin, large castingproducts which have been difficult to cast by the conventional methodcan be cast. In addition, as the present invention utilizes the superiorheat-insulating property of the generated gas, an expensive materialhaving superior heat insulation and heat retention is not particularlynecessary to use as the powdery inorganic material, thus a tremendouscost reduction may be achieved.

What is claimed is:
 1. A powdery mold-releasing lubricant for use incasting with a mold, comprising a powdery mixture of (a) a powderyorganic material which is evaporated or decomposed by heating togenerate 10-50 ml gas per 1 g of the mixture, and (b) a powderyinorganic material.
 2. A powdery mold-releasing lubricant according toclaim 1, wherein the powdery inorganic material is a powder of aninorganic material having a solid lubricity, said inorganic materialbeing selected from the group consisting of graphite, kaolinite, SHIRASU(pumice stone) balloons, mica, zirconium silicate, carbon nanotube,carbon isotopes, talc, pyrophylite, crystalline SiO₂, magnesium oxide,zirconium silicate, perlite and vermiculite.
 3. A powdery mold-releasinglubricant according to claim 1, wherein the powdery inorganic materialis a powder of an inorganic material having a solid lubricity, saidinorganic material being selected from the group consisting of graphite,kaolinite, SHIRASU (pumice stone) balloons, mica, and zirconiumsilicate.
 4. A powdery mold-releasing lubricant according to claim 1,wherein an average particle size of the powdery inorganic material inthe mixture is 1-30 μm.
 5. A powdery mold-releasing lubricant accordingto claim 1, wherein an average partical size of the powdery inorganicmaterial in the mixture is 1-30 μm.
 6. A powdery mold-releasinglubricant according to claim 1, wherein the powdery organic material isselected from the group consisting of polyethylene wax, metal soap,paraffin carbon hydride, sulfonic acid and sulfonic acid salt.
 7. Apowdery mold-releasing lubriant according to claim 1, wherein thepowdery organic material is selected from the group consisting ofpolyethylene wax, metal soap, paraffin carbon hydride, sulfonic acid andsilfonic acid salt.
 8. A powdery mold-releasing lubricant according toclaim 4, wherein the powdery organic material is selected from the groupconsisting of polyethylene wax, metal soap, paraffin carbon hydride,sulfonic acid and sulfonic acid salt.
 9. A powdery mold-releasinglubricant according to claim 5, wherein the powdery organic material isselected from the group consisting of polyethylene wax, metal soap,paraffin carbon hydride, sulfonic acid and sulfonic acid salt.
 10. Amold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 1 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.11. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 1 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.12. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 4 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.13. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 5 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.14. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 6 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.15. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 7 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.16. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 8 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.17. A mold casting method, comprising the steps of applying a powderymold-releasing lubricant according to claim 9 onto internal surfaces ofa molding cavity and/or an injection sleeve, and feeding a molten metalinto the molding cavity and/or the injection sleeve, whereby gas isgenerated from the mixture upon contacting between the fed molten metaland the lubricant, a gas-solid mixed layer of the generated gas and thepowdery inorganic material is used as a heat-insulating boundary layer.18. A mold casting method according to claim 10, wherein an amount ofthe powdery mold-releasing lubricant applied on the internal surfaces ofthe molding cavity and/or the injection sleeve is 0.01-10 g per 1 m²unit area of.
 19. A mold casting method according to claim 11, whereinan amount of the powdery mold-releasing lubricant applied on theinternal surfaces of the molding cavity and/or the injection sleeve is0.01-10 g per 1 m² unit area of.
 20. A mold casting method according toclaim 12, wherein an amount of the powdery mold-releasing lubricantapplied on the internal surfaces of the molding cavity and/or theinjection sleeve is 0.01-10 g per 1 m² unit area of.
 21. A mold castingmethod according to claim 13, wherein an amount of the powderymold-releasing lubricant applied on the internal surfaces of the moldingcavity and/or the injection sleeve is 0.01-10 g per 1 m² unit area of.22. A mold casting method according to claim 14, wherein an amount ofthe powdery mold-releasing lubricant applied on the internal surfaces ofthe molding cavity and/or the injection sleeve is 0.01-10 g per 1 m²unit area of.
 23. A mold casting method according to claim 15, whereinan amount of the powdery mold-releasing lubricant applied on theinternal surfaces of the molding cavity and/or the injection sleeve is0.01-10 g per 1 m² unit area of.
 24. A mold casting method according toclaim 16, wherein an amount of the powdery mold-releasing lubricantapplied on the internal surfaces of the molding cavity and/or theinjection sleeve is 0.01-10 g per 1 m² unit area of.
 25. A mold castingmethod according to claim 17, wherein an amount of the powderymold-releasing lubricant applied on the internal surfaces of the moldingcavity and/or the injection sleeve is 0.01-10 g per 1 m² unit area of.